This invention relates to engine exhaust driven turbochargers and, more particularly, to a turbocharger with connecting means that align, affix and thermally isolate stationary exhaust turbine section components from an adjoining support structure containing the rotor system and stationary compressor section components.
Continuing development of turbochargers is directed toward increasing efficiency over a greater range of operation at higher pressure ratios in smaller and more reliable configurations to improve engine fuel efficiency, reduce environmentally harmful exhaust emissions and minimize product cost. Improved turbocharger designs must endure significant cyclical thermal gradients between stationary turbine exhaust components and the rotor support structure. The turbine exhaust components include the stationary ducts used to convey engine exhaust gas through the turbine section to extract useful work and shroud the turbine section rotating components, thereby requiring concentric alignment. The rotor system comprises a rotor on which one or more compressors arranged for radial or axial air output are mounted in a coaxial arrangement with one or more turbines configured for radial or axial exhaust gas input. The rotor system is supported on two or more bearings either inboard or outboard of these mechanisms. Stationary compressor components mount to the rotor support and channel compressed inlet air away from the turbocharger. The need to utilize maximum exhaust energy available to the turbine section tends to conflict with the need to maintain rotor support bearings and compressed intake air at much lower relative temperatures. Improved means for aligning and thermally isolating the connected high and low temperature components are accordingly desired.
The present invention provides a turbocharger connection structure that thermally isolates stationary turbine components from a rotor support structure by minimizing contact between the two assemblies while maintaining concentric alignment of the rotor with the respect to the adjoining turbine components. In operation, the significantly hotter turbine components, such as the turbine exhaust duct, expand radially beyond the supporting rotor support dimensions by sliding about an array of fixed or replaceable pads that minimize heat transfer across the interface. Spring assemblies at each pad location moderate the clamp load against each pad to permit sliding across the joint without undue wear. A guide aligns each spring assembly and controls clamping force by limiting spring compression. As the pads wear, clamping force decreases very little due to minimal change in the spring force relative to deflection. The clamping force remains sufficient to keep the interface together, thereby maintaining a continuous constraint normal to the plane of the interface.
A minimum of three fixed or floating machined guides, comprising radially arrayed keys engaging mating slots in the connected members, constrain translational or rotational movement within clearances designed into the guides. Adjoining components, each containing half of the guide system, move relative to each other without losing rotor centerline alignment. This system of radial guides provides the sole means of alignment and support about the interface plane with no need for pilots or other alignment aids. The unique interface provided by the invention accomplishes the primary goals of turbine section alignment and joint durability while significantly impeding heat migration into the rotor support structure.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.